1. Field of the Invention
The present invention relates to a data input device having a switch matrix arrangement for detecting operated switches.
2. Discussion of the Prior Art
A keyboard of a typewriter is an example of an element which constitutes a data input device. The keyboard is equipped with a multiplicity of key switches (generally called keys), which are operated to enter data such as letters and symbols. The key switches produce output signals while the switches are held in their operated or depressed position. The keyboard may be equipped with some position-hold switches in addition to the multiple key switches. These position-hold switches have two or more stable positions and are held in a selected one of the stable positions. The position-hold switches produce output signals indicative of the selected stable position or selected state of the switching circuit. A selector switch for specifying a line spacing on a typewriter is an example of such a position-hold switch.
Commonly, determination of an operated one of multiple key switches is accomplished by scanning a switch matrix wherein first and second signal lines cross each other so as to provide intersecting points, wherein the key switches are connected between the first signal lines and the second signal lines (row signal lines and column signal lines) at respective interacting points. Usually, the number of position-hold switches provided on a data input device is considerably smaller than that of the key switches. For this reason, determination of a selected position of the position-hold switch is made by using exclusive signal lines.
However, a circuit arrangement for detecting the operated key switches and the selected positions of the position-hold switches in the above manner tends to be complicated in the hardware due to the use of the exclusive signal lines and the detecting circuit for the position-hold switches, in addition to the switch matrix for the key switches and matrix scanning circuit.